Free fluorine is composed of diatomic molecules. From the chemical point of view, fluorine can be characterized as a monovalent non-metal, and, moreover, the most active of all non-metals. This is due to a number of reasons, including the ease of disintegration of the F 2 molecule into individual atoms - the energy required for this is only 159 kJ / mol (versus 493 kJ / mol for O 2 and 242 kJ / mol for C 12). Fluorine atoms have significant electron affinity and relatively small size. Therefore, their valence bonds with atoms of other elements turn out to be stronger than similar bonds of other metalloids (for example, the H-F bond energy is - 564 kJ / mol versus 460 kJ / mol for the H-O bond and 431 kJ / mol for the H-C1 bond).

The F-F bond is characterized by a nuclear distance of 1.42 A. For the thermal dissociation of fluorine, the following data were obtained by calculation:

The fluorine atom has in the ground state the structure of the outer electron layer 2s 2 2p 5 and is univalent. Excitation of the trivalent state associated with the transfer of one 2p-electron to the 3s level requires an expenditure of 1225 kJ / mol and is practically not realized.

The electron affinity of a neutral fluorine atom is estimated at 339 kJ / mol. Ion F - is characterized by an effective radius of 1.33 A and a hydration energy of 485 kJ / mol. The covalent radius of fluorine is usually assumed to be 71 pm (that is, half the internuclear distance in the F 2 molecule).

Chemical bond is an electronic phenomenon, which consists in the fact that at least one electron, which was in the force field of its nucleus, finds itself in the force field of another nucleus or several nuclei at the same time.

Most simple substances and all complex substances (compounds) consist of atoms that interact with each other in a certain way. In other words, a chemical bond is established between atoms. When a chemical bond is formed, energy is always released, that is, the energy of the resulting particle must be less than the total energy of the original particles.

The transition of an electron from one atom to another, as a result of which oppositely charged ions with stable electronic configurations are formed, between which electrostatic attraction is established, is the simplest model of ionic bond:

X → X + + e -; Y + e - → Y -; X + Y -

The hypothesis of the formation of ions and the occurrence of electrostatic attraction between them was first put forward by the German scientist V. Kossel (1916).

Another communication model is the sharing of electrons by two atoms, as a result of which stable electronic configurations are also formed. Such a bond is called covalent. Its theory was started in 1916 by the American scientist G. Lewis.

The common point in both theories was the formation of particles with a stable electronic configuration, which coincides with the electronic configuration of a noble gas.

For example, when lithium fluoride is formed, the ionic mechanism of bond formation is realized. The lithium atom (3 Li 1s 2 2s 1) loses an electron and turns into a cation (3 Li + 1s 2) with the electronic configuration of helium. Fluorine (9 F 1s 2 2s 2 2p 5) accepts an electron, forming an anion (9 F - 1s 2 2s 2 2p 6) with the electronic configuration of neon. An electrostatic attraction arises between the lithium ion Li + and the fluorine ion F -, due to which a new compound is formed - lithium fluoride.

When hydrogen fluoride is formed, a single electron of a hydrogen atom (1s) and an unpaired electron of a fluorine atom (2p) are in the field of action of both nuclei - a hydrogen atom and a fluorine atom. Thus, a common electron pair appears, which means a redistribution of the electron density and the emergence of a maximum of the electron density. As a result, two electrons are now associated with the nucleus of the hydrogen atom (the electronic configuration of the helium atom), and with the nucleus of fluorine - eight electrons of the external energy level (the electronic configuration of the neon atom):

Communication carried out by means of one electronic pair is called a single bond.

It is denoted by a single dash between the element symbols: H-F.

The tendency to form a stable eight-electron shell by the transfer of an electron from one atom to another (ionic bond) or the socialization of electrons (covalent bond) is called the octet rule.

The formation of two-electron shells in a lithium ion and a hydrogen atom is a special case.

There are, however, connections that do not meet this rule. For example, the beryllium atom in beryllium fluoride BeF 2 has only a four-electron shell; six electron shells are characteristic of the boron atom (the dots indicate the electrons of the external energy level):

At the same time, in such compounds as phosphorus (V) chloride and sulfur (VI) fluoride, iodine (VII) fluoride, the electron shells of the central atoms contain more than eight electrons (phosphorus - 10; sulfur - 12; iodine - 14):

Most conjunctions of d-elements do not follow the octet rule either.

In all of the above examples, a chemical bond is formed between the atoms of different elements; it is called heteroatomic. However, a covalent bond can also form between identical atoms. For example, a hydrogen molecule is formed by the sharing of 15 electrons of each hydrogen atom, as a result of which each atom acquires a stable electronic configuration of two electrons. An octet is formed by the formation of molecules of other simple substances, for example, fluorine:

The formation of a chemical bond can also be carried out by the socialization of four or six electrons. In the first case, a double bond is formed, which is two generalized pairs of electrons, in the second - a triple bond (three generalized electron pairs).

For example, when a nitrogen molecule N 2 is formed, a chemical bond is formed by the socialization of six electrons: three unpaired p electrons from each atom. To achieve an eight-electron configuration, three common electron pairs are formed:

A double bond is indicated by two dashes, a triple bond by three. The nitrogen molecule N 2 can be represented as follows: N≡N.

In diatomic molecules formed by atoms of one element, the maximum electron density is located in the middle of the internuclear line. Since there is no separation of charges between atoms, this kind of covalent bond is called non-polar. The heteroatomic bond is always polar to one degree or another, since the maximum of the electron density is shifted towards one of the atoms, due to which it acquires a partial negative charge (denoted by σ-). The atom from which the maximum of the electron density is displaced acquires a partial positive charge (denoted by σ +). Electrically neutral particles in which the centers of partial negative and partial positive charges do not coincide in space are called dipoles. The polarity of the bond is measured by the dipole moment (μ), which is directly proportional to the magnitude of the charges and the distance between them.

Rice. Schematic representation of a dipole

List of used literature

1. Popkov V.A., Puzakov S. A. General chemistry: textbook. - M .: GEOTAR-Media, 2010 .-- 976 p .: ISBN 978-5-9704-1570-2. [with. 32-35]

In 1916, the first extremely simplified theories of the structure of molecules were proposed, in which electronic representations were used: the theory of the American physicochemist G. Lewis (1875-1946) and the German scientist V. Kossel. According to Lewis's theory, the valence electrons of two atoms at once participate in the formation of a chemical bond in a diatomic molecule. Therefore, for example, in the hydrogen molecule, instead of the valence prime, they began to draw an electron pair forming a chemical bond:

The chemical bond formed by an electron pair is called a covalent bond. The hydrogen fluoride molecule is depicted as follows:

The difference between molecules of simple substances (H2, F2, N2, O2) and molecules of complex substances (HF, NO, H2O, NH3) is that the former do not have a dipole moment, while the latter do. The dipole moment m is defined as the product of the absolute value of the charge q by the distance between two opposite charges r:

The dipole moment m of a diatomic molecule can be determined in two ways. First, since the molecule is electrically neutral, the total positive charge of the molecule Z "is known (it is equal to the sum of the charges of the atomic nuclei: Z" = ZA + ZB). Knowing the internuclear distance re, one can determine the location of the center of gravity of the positive charge of the molecule. The m value of the molecule is found from experiment. Therefore, you can find r "- the distance between the centers of gravity of the positive and total negative charge of the molecule:

Secondly, we can assume that when the electron pair forming a chemical bond is displaced to one of the atoms, some excess negative charge -q "appears on this atom and the charge + q" appears on the second atom. The distance between atoms is re:

The dipole moment of the HF molecule is 6.4 × 10-30 KL / m, the H-F internuclear distance is 0.917 × 10-10 m. Calculation of q "gives: q" = 0.4 of the elementary charge (ie the electron charge). Once an excess negative charge has appeared on the fluorine atom, it means that the electron pair forming a chemical bond in the HF molecule is displaced towards the fluorine atom. This chemical bond is called a covalent polar bond. Molecules of type A2 have no dipole moment. The chemical bonds forming these molecules are called covalent non-polar bonds.

Kossel's theory was proposed to describe molecules formed by active metals (alkali and alkaline earth) and active non-metals (halogens, oxygen, nitrogen). The outer valence electrons of metal atoms are the most distant from the nucleus of the atom and therefore are relatively weakly held by the metal atom. At atoms of chemical elements located in the same row of the Periodic Table, when passing from left to right, the charge of the nucleus increases all the time, and additional electrons are located in the same electron layer. This leads to the fact that the outer electron shell is compressed and the electrons are more and more firmly held in the atom. Therefore, in the MeX molecule, it becomes possible to move the weakly retained external valence electron of the metal with an energy expenditure equal to the ionization potential into the valence electron shell of the nonmetal atom with the release of energy equal to the electron affinity. As a result, two ions are formed: Me + and X-. The electrostatic interaction of these ions is the chemical bond. This type of connection was called ionic.

If we determine the dipole moments of MeX molecules in pairs, it turns out that the charge from a metal atom does not transfer completely to a nonmetal atom, and the chemical bond in such molecules is better described as a covalent strongly polar bond. Positive metal cations Me + and negative anions of non-metal atoms X- usually exist at the sites of the crystal lattice of crystals of these substances. But in this case, each positive metal ion primarily interacts electrostatically with the nearest nonmetal anions, then with metal cations, etc. That is, in ionic crystals, chemical bonds are delocalized and each ion ultimately interacts with all other ions included in the crystal, which is a giant molecule.

Along with well-defined characteristics of atoms, such as charges of atomic nuclei, ionization potentials, electron affinity, less definite characteristics are used in chemistry. One of them is electronegativity. It was introduced to science by the American chemist L. Pauling. Let us first consider the data on the first ionization potential and on the electron affinity for elements of the first three periods.

The regularities in the ionization potentials and the electron affinity are fully explained by the structure of the valence electron shells of atoms. An isolated nitrogen atom has a much lower electron affinity than alkali metal atoms, although nitrogen is an active non-metal. It is in molecules that, when interacting with atoms of other chemical elements, nitrogen proves that it is an active non-metal. This is what L. Pauling tried to do, introducing "electronegativity" as the ability of atoms of chemical elements to displace an electron pair towards themselves during the formation covalent polar bonds... The electronegativity scale for chemical elements was proposed by L. Pauling. He attributed the highest electronegativity in conventional dimensionless units to fluorine - 4.0 oxygen - 3.5, chlorine and nitrogen - 3.0, bromine - 2.8. The nature of the change in the electronegativity of atoms fully corresponds to those laws that are expressed in the Periodic Table. Therefore, the use of the concept " electronegativity"simply translates into another language those patterns in the change in the properties of metals and non-metals, which are already reflected in the Periodic Table.

Many metals in the solid state are almost perfectly formed crystals.... At the sites of the crystal lattice in the crystal are atoms or positive ions of metals. The electrons of those metal atoms, from which the positive ions were formed, are in the form of an electron gas in the space between the nodes of the crystal lattice and belong to all atoms and ions. It is they who determine the characteristic metallic luster, high electrical conductivity and thermal conductivity of metals. A type the chemical bond that socialized electrons carry out in a metal crystal is calledmetal bond.

In 1819, the French scientists P. Dulong and A. Petit experimentally established that the molar heat capacity of almost all metals in the crystalline state is equal to 25 J / mol. Now we can easily explain why this is so. The metal atoms in the nodes of the crystal lattice are in motion all the time - they make oscillatory movements. This complex movement can be decomposed into three simple oscillatory movements in three mutually perpendicular planes. Each oscillatory motion has its own energy and its own law of its change with increasing temperature - its own heat capacity. The limiting value of the heat capacity for any vibrational motion of atoms is equal to R - the Universal Gas Constant. Three independent vibrational motions of atoms in the crystal will correspond to a heat capacity equal to 3R. When metals are heated, starting from very low temperatures, their heat capacity increases from zero. At room and higher temperatures, the heat capacity of most metals reaches its maximum value - 3R.

When heated, the crystal lattice of metals is destroyed and they pass into a molten state. When heated further, the metals evaporate. In vapors, many metals exist in the form of Me2 molecules. In these molecules, metal atoms are capable of forming covalent non-polar bonds.

Fluorine is a chemical element (symbol F, atomic number 9), a non-metal that belongs to the group of halogens. It is the most active and electronegative substance. At normal temperature and pressure, the fluorine molecule is a pale yellow color with the formula F 2. Like other halogens, molecular fluoride is very dangerous and causes severe chemical burns on contact with the skin.

Usage

Fluorine and its compounds are widely used, including for the production of pharmaceuticals, agrochemicals, fuels and lubricants and textiles. is used for etching glass, and fluorine plasma is used for the production of semiconductor and other materials. Low concentrations of F ions in toothpaste and drinking water can help prevent tooth decay, while higher concentrations are found in some insecticides. Many general anesthetics are derivatives of hydrofluorocarbons. The 18 F isotope is a source of positrons for medical imaging by positron emission tomography, and uranium hexafluoride is used to separate uranium isotopes and obtain them for nuclear power plants.

Discovery history

Minerals containing fluorine compounds were known for many years before the isolation of this chemical element. For example, the mineral fluorspar (or fluorite), consisting of calcium fluoride, was described in 1530 by George Agricola. He noticed that it can be used as a flux - a substance that helps to lower the melting point of a metal or ore and helps to purify the desired metal. Therefore, fluorine got its Latin name from the word fluere ("to flow").

In 1670, glassblower Heinrich Schwanhard discovered that glass was etched by acid-treated calcium fluoride (fluorspar). Carl Scheele and many later researchers, including Humphrey Davy, Joseph-Louis Gay-Lussac, Antoine Lavoisier, Louis Thénard, experimented with hydrofluoric acid (HF), which was easy to obtain by treating CaF with concentrated sulfuric acid.

Eventually, it became clear that HF ​​contained a previously unknown element. However, due to its excessive reactivity, it was not possible to isolate this substance for many years. It is not only difficult to separate from the compounds, but it immediately reacts with their other components. The separation of elemental fluorine from hydrofluoric acid is extremely dangerous, and early attempts have blinded and killed several scientists. These people became known as the "fluoride martyrs."

Discovery and production

Finally, in 1886, the French chemist Henri Moissan was able to isolate fluorine by electrolysis of a mixture of molten potassium fluorides and hydrofluoric acid. For this he was awarded the 1906 Nobel Prize in Chemistry. Its electrolytic approach continues to be used today for the industrial production of this chemical element.

The first large-scale production of fluoride began during World War II. It was required for one of the stages of the atomic bomb creation as part of the Manhattan Project. Fluorine was used to produce uranium hexafluoride (UF 6), which in turn was used to separate the two isotopes 235 U and 238 U. Today, gaseous UF 6 is required to obtain enriched uranium for nuclear power.

The most important properties of fluorine

In the periodic table, the element is in the upper part of group 17 (formerly group 7A), which is called halogen. Other halogens include chlorine, bromine, iodine and astatine. In addition, F is in the second period between oxygen and neon.

Pure fluorine is a corrosive gas (chemical formula F 2) with a characteristic pungent odor, which is found at a concentration of 20 nl per liter of volume. As the most reactive and electronegative of all elements, it easily forms compounds with most of them. Fluorine is too reactive to exist in elemental form and has such an affinity for most materials, including silicon, that it cannot be cooked or stored in glass containers. In humid air, it reacts with water to form an equally dangerous hydrofluoric acid.

Fluorine, interacting with hydrogen, explodes even at low temperatures and in the dark. It reacts violently with water to form hydrofluoric acid and oxygen gas. Various materials, including finely dispersed metals and glass, burn brightly in a stream of gaseous fluorine. In addition, this chemical element forms compounds with the noble gases krypton, xenon and radon. However, it does not react directly with nitrogen and oxygen.

Despite the extreme activity of fluorine, methods for its safe handling and transport are now available. The element can be stored in containers made of steel or monel (a nickel-rich alloy), as fluorides form on the surface of these materials, which prevents further reaction.

Fluorides are substances in which fluorine is present as a negatively charged ion (F -) in combination with some positively charged elements. Fluorine compounds with metals are among the most stable salts. When dissolved in water, they are divided into ions. Other forms of fluorine are complexes, for example -, and H 2 F +.

Isotopes

There are many isotopes of this halogen, ranging from 14 F to 31 F. But the isotopic composition of fluorine includes only one of them, 19 F, which contains 10 neutrons, since only it is stable. The radioactive isotope 18 F is a valuable source of positrons.

Biological impact

Fluoride in the body is mainly found in bones and teeth in the form of ions. Fluoridation of drinking water at a concentration of less than one part per million significantly reduces the incidence of tooth decay, according to the National Research Council of the US National Academy of Sciences. On the other hand, excessive accumulation of fluoride can lead to fluorosis, which manifests itself as mottling of the teeth. This effect is usually observed in areas where the content of this chemical element in drinking water exceeds the concentration of 10 ppm.

Elemental fluoride and fluoride salts are toxic and must be handled with great care. Contact with skin or eyes should be carefully avoided. A reaction with the skin produces a tissue that quickly penetrates the tissues and reacts with the calcium in the bones, damaging them permanently.

Fluorine in the environment

The annual world production of the mineral fluorite is about 4 million tons, and the total capacity of the explored deposits is within 120 million tons. The main regions for the extraction of this mineral are Mexico, China and Western Europe.

Fluoride is naturally found in the earth's crust, where it can be found in rocks, coal, and clay. Fluorides are released into the air during wind erosion of soil. Fluorine is the 13th most abundant chemical element in the earth's crust - its content is 950 ppm. In soils, its average concentration is about 330 ppm. Hydrogen fluoride can be released into the air as a result of combustion processes in industry. Fluorides that are in the air will eventually fall to the ground or into the water. When fluorine forms a bond with very small particles, it can remain in the air for a long period of time.

In the atmosphere, 0.6 ppb of this chemical element is present in the form of salt fog and organic chlorine compounds. In urban environments, the concentration reaches 50 ppb.

Connections

Fluorine is a chemical element that forms a wide range of organic and inorganic compounds. Chemists can replace hydrogen atoms with it, thereby creating many new substances. The highly reactive halogen forms compounds with noble gases. In 1962, Neil Bartlett synthesized xenon hexafluoroplatinate (XePtF6). Krypton and radon fluorides have also been obtained. Another compound is argon fluoride, which is stable only at extremely low temperatures.

Industrial application

In its atomic and molecular state, fluorine is used for plasma etching in the manufacture of semiconductors, flat panel displays, and microelectromechanical systems. Hydrofluoric acid is used to etch glass in lamps and other products.

Along with some of its compounds, fluorine is an important component in the production of pharmaceuticals, agrochemicals, fuels and lubricants and textiles. The chemical element is required to produce halogenated alkanes (halons), which, in turn, have been widely used in air conditioning and refrigeration systems. Later, this use of chlorofluorocarbons was banned because they contribute to the destruction of the ozone layer in the upper atmosphere.

Sulfur hexafluoride is an extremely inert, non-toxic greenhouse gas. The production of low-friction plastics such as Teflon is impossible without fluorine. Many anesthetics (eg, sevoflurane, desflurane, and isoflurane) are derived from hydrofluorocarbons. Sodium hexafluoroaluminate (cryolite) is used in aluminum electrolysis.

Fluoride compounds, including NaF, are used in toothpastes to prevent tooth decay. These substances are added to municipal water supplies to fluoridate water, but the practice is considered controversial due to the impact on human health. At higher concentrations, NaF is used as an insecticide, especially for cockroach control.

In the past, fluorides have been used to reduce both ores and increase their fluidity. Fluorine is an important component in the production of uranium hexafluoride, which is used to separate its isotopes. 18 F, a radioactive isotope with 110 minutes, emits positrons and is often used in medical positron emission tomography.

Physical properties of fluorine

The basic characteristics of a chemical element are as follows:

• The atomic mass is 18.9984032 g / mol.
• Electronic configuration 1s 2 2s 2 2p 5.
• Oxidation state -1.
• Density 1.7 g / l.
• Melting point 53.53 K.
• The boiling point is 85.03 K.
• Heat capacity 31.34 J / (K mol).

Chemical particles formed from two or more atoms are called molecules(real or conditional formula units polyatomic substances). Atoms in molecules are chemically bonded.

Chemical bonding is understood as the electrical forces of attraction that hold particles near each other. Every chemical bond in structural formulas appears to valence trait, For example:

H - H (bond between two hydrogen atoms);

H 3 N - H + (the bond between the nitrogen atom of the ammonia molecule and the hydrogen cation);

(K +) - (I -) (bond between potassium cation and iodide ion).

A chemical bond is formed by a pair of electrons (), which in the electronic formulas of complex particles (molecules, complex ions) is usually replaced by a valence line, in contrast to their own, lone electron pairs of atoms, for example:

The chemical bond is called covalent, if it is formed by the socialization of a pair of electrons by both atoms.

In the F 2 molecule, both fluorine atoms have the same electronegativity, therefore, the possession of an electron pair is the same for them. Such a chemical bond is called non-polar, since each fluorine atom electron density is the same in electronic formula molecules can be divided equally between them:

In the hydrogen chloride HCl molecule, the chemical bond is already polar, since the electron density on the chlorine atom (an element with higher electronegativity) is much higher than on the hydrogen atom:

A covalent bond, for example H - H, can be formed by the sharing of electrons of two neutral atoms:

H + H> H - H

This bond formation mechanism is called exchange or equivalent.

According to another mechanism, the same covalent H - H bond arises when the electron pair of the hydride ion H is shared by the hydrogen cation H +:

H + + (: H) -> H - H

In this case, the H + cation is called acceptor, a anion H - donor electronic pair. The mechanism of formation of a covalent bond in this case will be donor-acceptor, or coordination.

Single bonds (H - H, F - F, H - CI, H - N) are called a-ties, they define the geometric shape of the molecules.

Double and triple bonds () contain one? -Component and one or two? -Components; The? -component, which is the main and conditionally formed first, is always stronger than? -components.

The physical (actually measurable) characteristics of a chemical bond are its energy, length and polarity.

Chemical bond energy (E sv) is the heat that is released during the formation of this bond and is spent on its breaking. For the same atoms, a single bond is always weaker than multiple (double, triple).

Chemical bond length (l cv) - internuclear distance. For the same atoms, a single bond is always longer than a multiple.

Polarity communication is measured electric dipole moment p- the product of the real electric charge (on the atoms of a given bond) by the length of the dipole (i.e., the length of the bond). The greater the dipole moment, the higher the polarity of the bond. Real electric charges on atoms in a covalent bond are always less in value than the oxidation states of the elements, but coincide in sign; for example, for the H + I -Cl -I bond, the real charges are equal to H +0 "17 -Cl -0" 17 (a bipolar particle, or a dipole).

Polarity of molecules is determined by their composition and geometric shape.

Non-polar (p = O) will be:

a) molecules simple substances, since they contain only non-polar covalent bonds;

b) polyatomic molecules complex substances, if their geometric shape symmetrical.

For example, CO 2, BF 3 and CH 4 molecules have the following directions of equal (in length) bond vectors:

When the bond vectors are added, their sum always vanishes, and the molecules as a whole are non-polar, although they contain polar bonds.

Polar (p> O) will be:

but) diatomic molecules complex substances, since they contain only polar bonds;

b) polyatomic molecules complex substances, if their structure asymmetric, that is, their geometric shape is either incomplete or distorted, which leads to the appearance of a total electric dipole, for example, in the molecules NH 3, H 2 O, HNO 3 and HCN.

Complex ions, for example NH 4 +, SO 4 2- and NO 3 -, cannot be dipoles in principle, they carry only one (positive or negative) charge.

Ionic bond arises from the electrostatic attraction of cations and anions with almost no socialization of a pair of electrons, for example, between K + and I -. The potassium atom has a lack of electron density, the iodine atom has an excess. This connection is believed ultimate the case of a covalent bond, since a pair of electrons is practically in possession of the anion. This relationship is most typical for compounds of typical metals and non-metals (CsF, NaBr, CaO, K 2 S, Li 3 N) and substances of the class of salts (NaNO 3, K 2 SO 4, CaCO 3). All these compounds under room conditions are crystalline substances, which are united by a common name ionic crystals(crystals built from cations and anions).

Another type of communication is known, called metal bond, in which valence electrons are so loosely held by metal atoms that they do not actually belong to specific atoms.

Metal atoms, left without clearly belonging to them external electrons, become, as it were, positive ions. They form metal crystal lattice. The set of shared valence electrons ( electronic gas) holds positive metal ions together and at specific lattice sites.

In addition to ionic and metallic crystals, there are also atomic and molecular crystalline substances, in the lattice sites of which there are atoms or molecules, respectively. Examples: diamond and graphite - crystals with an atomic lattice, iodine I 2 and carbon dioxide CO 2 (dry ice) - crystals with a molecular lattice.

Chemical bonds exist not only within the molecules of substances, but can also form between molecules, for example, for liquid HF, water H 2 O and a mixture of H 2 O + NH 3:

Hydrogen bond formed due to the forces of electrostatic attraction of polar molecules containing atoms of the most electronegative elements - F, O, N. For example, hydrogen bonds are present in HF, H 2 O and NH 3, but they are not in HCl, H 2 S and PH 3.

Hydrogen bonds are unstable and break quite easily, for example, when ice melts and water boils. However, breaking these bonds requires some additional energy, and therefore the melting points (Table 5) and boiling points of substances with hydrogen bonds

(for example, HF and H 2 O) turn out to be significantly higher than for similar substances, but without hydrogen bonds (for example, HCl and H 2 S, respectively).

Many organic compounds also form hydrogen bonds; hydrogen bonding plays an important role in biological processes.

Examples of assignments for part A

1. Substances with only covalent bonds are

1) SiH 4, Cl 2 O, CaBr 2

2) NF 3, NH 4 Cl, P 2 O 5

3) CH 4, HNO 3, Na (CH 3 O)

4) CCl 2 O, I 2, N 2 O

2–4. Covalent bond

2.single

3.double

4.triple

present in the substance

5. Multiple bonds exist in molecules

6. Particles called radicals are

7. One of the bonds is formed by the donor-acceptor mechanism in the set of ions

1) SO 4 2-, NH 4 +

2) H 3 O +, NH 4 +

3) PO 4 3-, NO 3 -

4) PH 4 +, SO 3 2-

8. The most durable and short bond - in a molecule

9. Substances with ionic bonds only - in a set

2) NH 4 Cl, SiCl 4

10–13. Crystal lattice of matter

13. Wa (OH) 2

1) metal

Task number 1

From the proposed list, select two compounds in which an ionic chemical bond is present.

• 1. Ca (ClO 2) 2
• 2. HClO 3
• 3. NH 4 Cl
• 4. HClO 4
• 5. Cl 2 O 7

Answer: 13

In the overwhelming majority of cases, it is possible to determine the presence of an ionic type of bond in a compound by the fact that the composition of its structural units simultaneously includes atoms of a typical metal and atoms of a non-metal.

On this basis, we establish that there is an ionic bond in the compound under number 1 - Ca (ClO 2) 2, since in its formula you can see the atoms of a typical metal calcium and atoms of non-metals - oxygen and chlorine.

However, there are no more compounds containing both metal and non-metal atoms in this list.

Among the compounds specified in the task there is ammonium chloride, in which the ionic bond is realized between the ammonium cation NH 4 + and the chloride ion Cl -.

Task number 2

From the list provided, select two compounds in which the type of chemical bond is the same as in the fluorine molecule.

1) oxygen

2) nitric oxide (II)

3) hydrogen bromide

4) sodium iodide

Write down the numbers of the selected connections in the answer field.

Answer: 15

A fluorine molecule (F 2) consists of two atoms of one chemical element of a non-metal, therefore the chemical bond in this molecule is covalent non-polar.

A covalent non-polar bond can be realized only between atoms of the same chemical element of a non-metal.

Of the proposed options, only oxygen and diamond have a covalent non-polar bond. The oxygen molecule is diatomic, it consists of atoms of one chemical element of a non-metal. Diamond has an atomic structure and in its structure, each carbon atom, which is a non-metal, is bonded to 4 other carbon atoms.

Nitric oxide (II) is a substance consisting of molecules formed by atoms of two different non-metals. Since the electronegativities of different atoms are always different, the total electron pair in a molecule is shifted towards a more electronegative element, in this case oxygen. Thus, the bond in the NO molecule is covalent polar.

Hydrogen bromide also consists of diatomic molecules composed of hydrogen and bromine atoms. The common electron pair forming the H-Br bond is shifted towards the more electronegative bromine atom. The chemical bond in the HBr molecule is also covalent polar.

Sodium iodide is an ionic substance formed by a metal cation and an iodide anion. The bond in the NaI molecule is formed due to the transition of an electron from 3 s-orbital of the sodium atom (the sodium atom turns into a cation) to the underfilled 5 p-orbital of the iodine atom (the iodine atom turns into an anion). This chemical bond is called ionic.

Task number 3

From the proposed list, select two substances between the molecules of which hydrogen bonds are formed.

• 1.C 2 H 6
• 2.C 2 H 5 OH
• 3. H 2 O
• 4. CH 3 OCH 3
• 5.CH 3 COCH 3

Write down the numbers of the selected connections in the answer field.

Answer: 23

Explanation:

Hydrogen bonds take place in substances of molecular structure, in which covalent bonds H-O, H-N, H-F are present. Those. covalent bonds of a hydrogen atom with atoms of three chemical elements with the highest electronegativity.

Thus, obviously, there are hydrogen bonds between molecules:

2) alcohols

3) phenols

4) carboxylic acids

5) ammonia

6) primary and secondary amines

7) hydrofluoric acid

Task number 4

Select two compounds with ionic chemical bonds from the list.

• 1.PCl 3
• 2.CO 2
• 3. NaCl
• 4.H 2 S
• 5. MgO

Write down the numbers of the selected connections in the answer field.

Answer: 35

Explanation:

In the overwhelming majority of cases, it is possible to draw a conclusion about the presence of an ionic type of bond in a compound by the fact that the structural units of a substance simultaneously include atoms of a typical metal and atoms of a non-metal.

On this basis, we establish that there is an ionic bond in the compound numbered 3 (NaCl) and 5 (MgO).

Note*

In addition to the above sign, the presence of an ionic bond in a compound can be said if its structural unit contains an ammonium cation (NH 4 +) or its organic analogs - alkylammonium cations RNH 3 +, dialkylammonium R 2 NH 2 +, trialkylammonium R 3 NH + or tetraalkylammonium R 4 N +, where R is some hydrocarbon radical. For example, the ionic type of bond occurs in the compound (CH 3) 4 NCl between the cation (CH 3) 4 + and the chloride ion Cl -.

Task number 5

From the proposed list, select two substances with the same type of structure.

4) table salt

Write down the numbers of the selected connections in the answer field.

Answer: 23

Task number 8

Select two substances of non-molecular structure from the proposed list.

2) oxygen

3) white phosphorus

5) silicon

Write down the numbers of the selected connections in the answer field.

Answer: 45

Task number 11

From the proposed list, select two substances in the molecules of which there is a double bond between carbon and oxygen atoms.

3) formaldehyde

4) acetic acid

5) glycerin

Write down the numbers of the selected connections in the answer field.

Answer: 34

Task number 14

From the proposed list, select two substances with an ionic bond.

1) oxygen

3) carbon monoxide (IV)

4) sodium chloride

5) calcium oxide

Write down the numbers of the selected connections in the answer field.

Answer: 45

Task number 15

From the proposed list, select two substances with the same type of crystal lattice as that of a diamond.

1) silica SiO 2

2) sodium oxide Na 2 O

3) carbon monoxide CO

4) white phosphorus P 4

5) silicon Si

Write down the numbers of the selected connections in the answer field.

Answer: 15

Task number 20

From the proposed list, select two substances in the molecules of which there is one triple bond.

• 1. HCOOH
• 2. HCOH
• 3.C 2 H 4
• 4.N 2
• 5.C 2 H 2

Write down the numbers of the selected connections in the answer field.

Answer: 45

Explanation:

In order to find the correct answer, let's draw the structural formulas of compounds from the list presented:

Thus, we see that there is a triple bond in the nitrogen and acetylene molecules. Those. correct answers 45

Task number 21

From the proposed list, select two substances in the molecules of which there is a covalent non-polar bond.

Themes of the USE codifier: Covalent chemical bond, its varieties and mechanisms of formation. Covalent bond characteristics (polarity and bond energy). Ionic bond. Metallic bond. Hydrogen bond

Intramolecular chemical bonds

First, consider the bonds that arise between particles within molecules. Such connections are called intramolecular.

Chemical bond between the atoms of chemical elements has an electrostatic nature and is formed due to interactions of external (valence) electrons, in more or less degree held by positively charged nuclei bonded atoms.

The key concept here is ELECTRIC NEGATIVITY. It is she who determines the type of chemical bond between atoms and the properties of this bond.

Is the ability of an atom to attract (hold) external(valence) electrons... Electronegativity is determined by the degree of attraction of external electrons to the nucleus and depends mainly on the radius of the atom and the charge of the nucleus.

Electronegativity is difficult to define unambiguously. L. Pauling compiled a table of relative electronegativities (based on the bond energies of diatomic molecules). The most electronegative element is fluorine with the meaning 4 .

It is important to note that in different sources you can find different scales and tables of values ​​of electronegativity. This should not be scared, since it plays a role in the formation of a chemical bond atoms, and it is about the same in any system.

If one of the atoms in the chemical bond A: B attracts electrons more strongly, then the electron pair is displaced towards it. The more difference of electronegativities atoms, the more the electron pair is displaced.

If the values ​​of the electronegativities of the interacting atoms are equal or approximately equal: EO (A) ≈EO (B), then the total electron pair is not shifted to any of the atoms: A: B... This connection is called covalent non-polar.

If the electronegativities of the interacting atoms differ, but not much (the difference in electronegativities is about 0.4 to 2: 0,4<ΔЭО<2 ), then the electron pair is shifted to one of the atoms. This connection is called covalent polar .

If the electronegativities of the interacting atoms differ significantly (the difference in electronegativities is greater than 2: ΔEO> 2), then one of the electrons is almost completely transferred to the other atom, with the formation ions... This connection is called ionic.

The main types of chemical bonds are - covalent, ionic and metal communication. Let's consider them in more detail.

Covalent chemical bond

Covalent bond – it is a chemical bond formed by formation of a common electron pair A: B ... In this case, two atoms overlap atomic orbitals. A covalent bond is formed by the interaction of atoms with a small difference in electronegativities (as a rule, between two non-metals) or atoms of one element.

Basic properties of covalent bonds

• focus,
• saturability,
• polarity,
• polarizability.

These bonding properties affect the chemical and physical properties of substances.

Direction of communication characterizes the chemical structure and form of substances. The angles between two bonds are called bond angles. For example, in a water molecule the H-O-H bond angle is 104.45 о, therefore the water molecule is polar, and in a methane molecule the H-C-H bond angle is 108 о 28 ′.

Saturability Is the ability of atoms to form a limited number of covalent chemical bonds. The number of bonds that an atom can form is called.

Polarity bond arises from the uneven distribution of electron density between two atoms with different electronegativity. Covalent bonds are divided into polar and non-polar.

Polarizability connections are ability of bond electrons to displace under the influence of an external electric field(in particular, the electric field of another particle). The polarizability depends on the electron mobility. The farther the electron is from the nucleus, the more mobile it is, and, accordingly, the molecule is more polarizable.

Covalent non-polar chemical bond

There are 2 types of covalent bonding - POLAR and NON-POLAR .

Example . Consider the structure of the hydrogen molecule H 2. Each hydrogen atom at the outer energy level carries 1 unpaired electron. To display the atom, we use the Lewis structure - this is a diagram of the structure of the external energy level of the atom, when electrons are denoted by dots. The Lewis point structure models are helpful when working with elements of the second period.

H. +. H = H: H

Thus, the hydrogen molecule has one common electron pair and one chemical bond H – H. This electron pair is not shifted to any of the hydrogen atoms, because the electronegativity of hydrogen atoms is the same. This connection is called covalent non-polar .

Covalent non-polar (symmetric) bond Is a covalent bond formed by atoms with equal electronegativity (as a rule, the same non-metals) and, therefore, with a uniform distribution of electron density between the nuclei of atoms.

The dipole moment of non-polar bonds is 0.

Examples of: H 2 (H-H), O 2 (O = O), S 8.

Covalent polar chemical bond

Covalent polar bond Is a covalent bond that occurs between atoms with different electronegativity (usually, different non-metals) and is characterized by displacement a common electron pair to a more electronegative atom (polarization).

The electron density is shifted to a more electronegative atom - therefore, a partial negative charge (δ-) arises on it, and a partial positive charge (δ +, delta +) arises on a less electronegative atom.

The greater the difference in the electronegativities of atoms, the higher polarity connections and all the more dipole moment ... Additional attractive forces act between neighboring molecules and charges of opposite sign, which increases strength communication.

The polarity of a bond affects the physical and chemical properties of compounds. The reaction mechanisms and even the reactivity of neighboring bonds depend on the polarity of the bond. The polarity of the connection often determines molecule polarity and thus directly affects physical properties such as boiling point and melting point, solubility in polar solvents.

Examples: HCl, CO 2, NH 3.

Mechanisms of covalent bond formation

A covalent chemical bond can occur through 2 mechanisms:

1. Exchange mechanism the formation of a covalent chemical bond is when each particle provides one unpaired electron for the formation of a common electron pair:

BUT . + . B = A: B

2. covalent bond formation is a mechanism in which one of the particles provides a lone electron pair, and the other particle provides a vacant orbital for this electron pair:

BUT: + B = A: B

In this case, one of the atoms provides a lone electron pair ( donor), and another atom provides a vacant orbital for this pair ( acceptor). As a result of bond formation, both the electron energy decreases, i.e. it is beneficial for atoms.

A covalent bond formed by the donor-acceptor mechanism is not different in properties from other covalent bonds formed by the exchange mechanism. The formation of a covalent bond by the donor-acceptor mechanism is typical for atoms with either a large number of electrons at the external energy level (electron donors), or vice versa, with a very small number of electrons (electron acceptors). The valence capabilities of atoms are discussed in more detail in the corresponding section.

A covalent bond by the donor-acceptor mechanism is formed:

- in a molecule carbon monoxide CO(the bond in the molecule is triple, 2 bonds are formed by the exchange mechanism, one by the donor-acceptor mechanism): C≡O;

- in ammonium ion NH 4 +, in ions organic amines, for example, in the methylammonium ion CH 3 -NH 2 +;

- in complex compounds, a chemical bond between the central atom and ligand groups, for example, in sodium tetrahydroxoaluminate Na the bond between aluminum and hydroxide ions;

- in nitric acid and its salts- nitrates: HNO 3, NaNO 3, in some other nitrogen compounds;

- in a molecule ozone O 3.

Main characteristics of a covalent bond

A covalent bond is usually formed between nonmetal atoms. The main characteristics of a covalent bond are length, energy, multiplicity and direction.

Multiplicity of chemical bond

Multiplicity of chemical bond - This the number of common electron pairs between two atoms in a compound... The multiplicity of the bond can be easily determined from the value of the atoms that form the molecule.

For example , in the hydrogen molecule H 2, the bond multiplicity is 1, since each hydrogen has only 1 unpaired electron at the external energy level, therefore, one common electron pair is formed.

In the oxygen molecule O 2, the bond multiplicity is 2, since each atom on the external energy level has 2 unpaired electrons: O = O.

In a nitrogen molecule N 2, the bond multiplicity is 3, since between each atom there are 3 unpaired electrons at the external energy level, and the atoms form 3 common electron pairs N≡N.

Covalent bond length

Chemical bond length Is the distance between the centers of the nuclei of the atoms that form the bond. It is determined by experimental physical methods. The bond length can be estimated approximately according to the additivity rule, according to which the bond length in the AB molecule is approximately equal to the half-sum of the bond lengths in the A2 and B2 molecules:

The length of the chemical bond can be roughly estimated along the radii of atoms forming a bond, or by the frequency of communication if the radii of the atoms are not very different.

With an increase in the radii of the atoms forming a bond, the bond length will increase.

For example

With an increase in the multiplicity of the bond between atoms (whose atomic radii do not differ, or differ insignificantly), the bond length will decrease.

For example ... In the series: C – C, C = C, C≡C, the bond length decreases.

Communication energy

The bond energy is a measure of the strength of a chemical bond. Communication energy is determined by the energy required to break a bond and remove the atoms that form this bond at an infinitely large distance from each other.

A covalent bond is very durable. Its energy ranges from several tens to several hundred kJ / mol. The higher the bond energy, the greater the bond strength, and vice versa.

The strength of a chemical bond depends on the bond length, bond polarity and bond multiplicity. The longer the chemical bond, the easier it is to break it, and the lower the bond energy, the lower its strength. The shorter the chemical bond, the stronger it is, and the greater the bond energy.

For example, in the series of compounds HF, HCl, HBr, from left to right, the strength of the chemical bond decreases since the length of the connection increases.

Ionic chemical bond

Ionic bond Is a chemical bond based on electrostatic attraction of ions.

Jonah are formed in the process of accepting or giving up electrons by atoms. For example, the atoms of all metals weakly retain electrons of the external energy level. Therefore, metal atoms are characterized by restorative properties- the ability to donate electrons.

Example. The sodium atom contains 1 electron at the 3rd energy level. Giving it up easily, the sodium atom forms a much more stable Na + ion, with the electronic configuration of the noble neon gas Ne. The sodium ion contains 11 protons and only 10 electrons, so the total charge of the ion is -10 + 11 = +1:

+11Na) 2) 8) 1 - 1e = +11 Na +) 2 ) 8

Example. The chlorine atom at the outer energy level contains 7 electrons. To acquire the configuration of a stable inert argon atom Ar, chlorine needs to attach 1 electron. After the attachment of an electron, a stable chlorine ion is formed, consisting of electrons. The total charge of the ion is -1:

+17Cl) 2) 8) 7 + 1e = +17 Cl — ) 2 ) 8 ) 8

Note:

• The properties of ions are different from the properties of atoms!
• Stable ions can form not only atoms, but also groups of atoms... For example: ammonium ion NH 4 +, sulfate ion SO 4 2-, etc. Chemical bonds formed by such ions are also considered ionic;
• The ionic bond, as a rule, is formed with each other metals and non-metals(groups of non-metals);

The formed ions are attracted due to electric attraction: Na + Cl -, Na 2 + SO 4 2-.

Let's summarize distinction between covalent and ionic bond types:

Metallic chemical bond

Metallic bond Is a connection that is formed relatively free electrons between metal ions forming a crystal lattice.

Metal atoms on the external energy level are usually located one to three electrons... The radii of metal atoms, as a rule, are large - therefore, metal atoms, in contrast to non-metals, donate external electrons quite easily, i.e. are strong reducing agents

Intermolecular interactions

Separately, it is worth considering the interactions that arise between individual molecules in a substance - intermolecular interactions ... Intermolecular interactions are a type of interaction between neutral atoms in which new covalent bonds do not appear. The forces of interaction between molecules were discovered by van der Waals in 1869 and named after him Van Dar Waals forces... The van der Waals forces are divided into orientation, induction and dispersive ... The energy of intermolecular interactions is much less than the energy of a chemical bond.

Orientational forces of gravity occur between polar molecules (dipole-dipole interaction). These forces arise between polar molecules. Induction interactions Is the interaction between a polar molecule and a non-polar one. A non-polar molecule is polarized due to the action of a polar one, which generates additional electrostatic attraction.

A special type of intermolecular interaction is hydrogen bonds. - these are intermolecular (or intramolecular) chemical bonds that arise between molecules in which there are strongly polar covalent bonds - H-F, H-O or H-N... If there are such bonds in a molecule, then between the molecules there will be additional forces of gravity .

Formation mechanism hydrogen bonding is partly electrostatic and partly donor – acceptor. In this case, the donor of the electron pair is the atom of a strongly electronegative element (F, O, N), and the acceptor is the hydrogen atoms connected to these atoms. The hydrogen bond is characterized by focus in space and saturation.

The hydrogen bond can be denoted by dots: Н ··· O. The greater the electronegativity of the atom, combined with hydrogen, and the smaller its size, the stronger the hydrogen bond. It is characteristic primarily of compounds fluorine with hydrogen and also to oxygen with hydrogen , less nitrogen with hydrogen .

Hydrogen bonds arise between the following substances:

— hydrogen fluoride HF(gas, solution of hydrogen fluoride in water - hydrofluoric acid), water H 2 O (steam, ice, liquid water):

— solution of ammonia and organic amines- between ammonia and water molecules;

— organic compounds in which O-H or N-H bonds: alcohols, carboxylic acids, amines, amino acids, phenols, aniline and its derivatives, proteins, solutions of carbohydrates - monosaccharides and disaccharides.

The hydrogen bond affects the physical and chemical properties of substances. Thus, additional attraction between molecules makes it difficult for substances to boil. For substances with hydrogen bonds, an abnormal increase in the boiling point is observed.

For example , as a rule, with an increase in molecular weight, an increase in the boiling point of substances is observed. However, in a number of substances H 2 O-H 2 S-H 2 Se-H 2 Te we do not observe a linear change in boiling points.

Namely, at water boiling point abnormally high - not less than -61 o C, as the straight line shows us, but much more, +100 o C. This anomaly is explained by the presence of hydrogen bonds between water molecules. Therefore, under normal conditions (0-20 ° C), water is liquid by phase state.

Atom, molecule, nuclear properties

The structure of the fluorine atom.

At the center of the atom is a positively charged nucleus. 9 negatively charged electrons revolve around.

Electronic formula: 1s2; 2s2; 2p5

m prot. = 1.00783 (amu)

m neutr. = 1.00866 (amu)

m proton = m electron

Fluorine isotopes.

Isotope: 18F

Brief description: Prevalence in nature: 0%

The number of protons in the nucleus - 9. The number of neutrons in the nucleus - 9. The number of nucleons - 18.E bonds = 931.5 (9 * m sp. + 9 * m neutr-M (F18)) = 138.24 (MEW) E specific = E bond / N nucleons = 7.81 (MeV / nucleon.)

Alpha decay not possible Beta minus decay impossible Positron decay: F ​​(Z = 9, M = 18) -> O (Z = 8, M = 18) + e (Z = + 1, M = 0) +0.28 ( MeV) Electron capture: F (Z = 9, M = 18) + e (Z = -1, M = 0) -> O (Z = 8, M = 18) +1.21 (MeV)

Isotope: 19F

Brief description: Prevalence in nature: 100%

Fluorine molecule.

Free fluorine is composed of diatomic molecules. From the chemical point of view, fluorine can be characterized as a monovalent non-metal, and, moreover, the most active of all non-metals. This is due to a number of reasons, including the ease of disintegration of the F2 molecule into individual atoms - the energy required for this is only 159 kJ / mol (versus 493 kJ / mol for O2 and 242 kJ / mol for C12). Fluorine atoms have significant electron affinity and relatively small size. Therefore, their valence bonds with atoms of other elements turn out to be stronger than similar bonds of other metalloids (for example, the H-F bond energy is - 564 kJ / mol versus 460 kJ / mol for the H-O bond and 431 kJ / mol for the H-C1 bond).

The F-F bond is characterized by a nuclear distance of 1.42 A. For the thermal dissociation of fluorine, the following data were obtained by calculation:

Temperature, ° С 300 500 700 900 1100 1300 1500 1700

Dissociation degree,% 5 10-3 0.3 4.2 22 60 88 97 99

The fluorine atom has in the ground state the structure of the outer electron layer 2s22p5 and is univalent. Excitation of the trivalent state associated with the transfer of one 2p-electron to the 3s level requires an expenditure of 1225 kJ / mol and is practically not realized. The electron affinity of a neutral fluorine atom is estimated at 339 kJ / mol. The F- ion is characterized by an effective radius of 1.33 A and a hydration energy of 485 kJ / mol. The covalent radius of fluorine is usually assumed to be 71 pm (that is, half the internuclear distance in the F2 molecule).

Chemical properties of fluorine.

Since fluoride derivatives of metalloid elements are usually highly volatile, their formation does not protect the metalloid surface from further action of fluorine. Therefore, the interaction often proceeds much more energetically than with many metals. For example, silicon, phosphorus and sulfur are ignited in fluorine gas. Amorphous carbon (charcoal) behaves similarly, while graphite reacts only at red heat. Fluorine does not directly combine with nitrogen and oxygen.

From the hydrogen compounds of other elements, fluorine takes away hydrogen. Most oxides are decomposed by it displacing oxygen. In particular, water interacts according to the scheme F2 + Н2О -> 2 НF + O

moreover, the displaced oxygen atoms combine not only with each other, but partially also with water and fluorine molecules. Therefore, in addition to gaseous oxygen, this reaction always produces hydrogen peroxide and fluorine oxide (F2O). The latter is a pale yellow gas that smells like ozone.

Fluorine oxide (otherwise - oxygen fluoride - ОF2) can be obtained by passing fluorine in 0.5 N. NaOH solution. The reaction proceeds according to the equation: 2 F2 + 2 NaOH = 2 NaF + Н2О + F2О The following reactions are also characteristic of fluorine:

H2 + F2 = 2HF (burst)

Chemistry preparation for ZNO and DPA
Complex edition

PART I

GENERAL CHEMISTRY

CHEMISTRY OF ELEMENTS

HALOGENS

Simple substances

Fluorine chemical properties

Fluorine is the strongest oxidizing agent in nature. It does not directly react only with helium, neon and argon.

Under the reaction time with metals, fluorides are formed, compounds of the ionic type:

Fluorine reacts vigorously with many non-metals, even with some inert gases:

Chlorine chemical properties. Interaction with complex substances

Chlorine is a stronger oxidizer than bromine or iodine, so chlorine displaces heavy halogens from their salts:

Dissolving in water, chlorine partially reacts with it, resulting in the formation of two acids: chloride and hypochlorite. In this case, one Chlorine atom increases the oxidation state, and the other atom decreases it. Such reactions are called disproportionate reactions. Disproportionate reactions are self-healing-self-oxidation reactions, i.e. reactions in which one element exhibits the properties of both an oxidizer and a reducing agent. When disproportionate, compounds are simultaneously formed in which the element is in a more oxidized and reduced state in comparison with the primitive one. The oxidation state of the Chlorine atom in the hypochlorite acid molecule is +1:

The interaction of chlorine with alkali solutions proceeds in a similar way. In this case, two salts are formed: chloride and hypochlorite.

Chlorine interacts with various oxides:

Chlorine oxidizes some salts in which the metal is not in the maximum oxidation state:

Molecular chlorine reacts with many organic compounds. In the presence of ferrum (III) chloride as a catalyst, chlorine reacts with benzene to form chlorobenzene, and upon irradiation with light, hexachlorocyclohexane is formed as a result of the same reaction:

Chemical properties of bromine and iodine

Both substances react with hydrogen, fluorine and alkalis:

Iodine is oxidized by various strong oxidants:

Methods for the extraction of simple substances

Extraction of fluorine

Since fluorine is the strongest chemical oxidizer, it is impossible to isolate it by means of chemical reactions from compounds in a free form, and therefore fluorine is extracted by a physicochemical method - electrolysis.

To extract fluorine, potassium fluoride melt and nickel electrodes are used. Nickel is used due to the fact that the metal surface is passivated by fluorine due to the formation of insoluble NiF 2, therefore, the electrodes themselves are not destroyed under the action of the substance that is released on them:

Chlorine extraction

Chlorine is produced on an industrial scale by electrolysis of sodium chloride solution. As a result of this process, sodium hydroxide is also mined:

Chlorine is extracted in small quantities by oxidized hydrogen chloride solution by various methods:

Chlorine is a very important product of the chemical industry.

Its world production is in the millions of tons.

Extraction of bromine and iodine

For industrial use, bromine and iodine are mined by oxidizing bromides and iodides, respectively. Molecular chlorine, concentrated sulfate acid or mangan dioxide are most often used for oxidation:

Application of halogens

Fluorine and some of its compounds are used as an oxidizing agent for rocket fuel. Large amounts of fluorine are used to extract various refrigerants (freons) and some polymers that are chemically and thermally stable (Teflon and some others). Fluorine is used in nuclear technology to separate uranium isotopes.

Most of the chlorine is used for the production of hydrochloric acid and also as an oxidizing agent for the production of other halogens. In industry it is used for bleaching fabrics and paper. In larger quantities than fluorine, it is used for the production of polymers (PVC and others) and refrigerants. With the help of chlorine, drinking water is disinfected. It is also needed to extract some solvents such as chloroform, methylene chloride, carbon tetrachloride. It is also used for the production of many substances, such as potassium chlorate (Berthollet's salt), bleach and many other compounds containing Chlorine atoms.

Bromine and iodine are not used in industry on the same scale as chlorine or fluorine, but the use of these substances is increasing every year. Bromine is used in the manufacture of various medicinal preparations with a calming effect. Iodine is used in the manufacture of antiseptic preparations. Bromine and Iodine compounds are widely used in the quantitative analysis of substances. With the help of iodine, some metals are purified (this process is called iodine refining), for example, titanium, vanadium and others.